Interior Secretary Ryan Zinke is reassigning dozens of top career officials within his ranks, a shake-up that appears to be the start of a broad reorganization of a department that manages one-fifth of all land within the United States.

The decision to move members of the Senior Executive Service (SES) is legally permitted only after a political appointee has been in office for 120 days; Zinke won’t reach that mark until June 28. But the letters that three dozen or more Interior officials got Thursday night — one of which was obtained by The Washington Post — provides them with 15 days notice of their job change. The notice means their reassignments could take place at the earliest date that is legally permissible.

An official with the Senior Executives Association, which represents 6,000 of the government’s top leaders, said the reassignments at Interior could involve as many as 50 people.

The shake-up comes two weeks before agencies across the government must submit initial plans to the White House showing how they intend to reorganize, reduce their workforce, assess which programs are necessary and look for changes that save money.

The exact number of Interior letters sent was not immediately clear Friday, but the push appears much broader than what Republican and Democratic administrations have pursued in the past. Administrations usually wait until the Senate has confirmed appointees that oversee individual agencies within a department; at this point, Zinke remains Interior’s only Senate-confirmed appointee.

“The President signed an executive order to reorganize the federal government for the future and the Secretary has been absolutely out front on that issue,” Interior spokeswoman Heather Swift said in an email. “Personnel moves are being conducted to better serve the taxpayer and the Department’s operations through matching Senior Executive skill sets with mission and operational requirements.”

The officials who received notices include Interior’s top climate policy official, Joel Clement, who directs the Office of Policy Analysis, as well as at least five senior officials of the Fish and Wildlife Service — nearly a quarter of that agency’s career SES staff. Among the Fish and Wildlife officials are the assistant director for international affairs, Bryan Arroyo; the Southwest regional director, Benjamin Tuggle; and the Southeast regional director, Cindy Dohner.

Other moves include the transfer of the Bureau of Land Management’s New Mexico state director, Amy Lueders, to Fish and Wildlife, and the reassignment of Bureau of Indian Affairs Director Weldon “Bruce” Loudermilk, acting assistant secretary of Indian affairs Michael S. Black and acting special trustee for American Indians Debra L. DuMontier. Some National Park Service leaders also are being reassigned.

Dan Ashe, who headed the Fish and Wildlife Service under the Obama administration and worked at the agency for more than two decades, said in an interview that having closely watched every transition since Ronald Reagan took the helm of the federal government from Jimmy Carter in 1981, “anything at this scale is unprecedented.”

“I’ve never seen anything like it,” Ashe said, adding that the officials being moved from posts at Fish and Wildlife “have records of exceptional service.”

The Senior Executive Service was established in 1978 “to create a mobile group of senior executives who could take on the most important, complicated jobs in the government,” according to Max Stier, president and chief executive of the nonprofit Partnership for Public Service.

Stier said Friday that while the idea was to move these officials among agencies and better compensate them, “it never fulfilled that vision” because pay caps meant they got more responsibility without additional pay. Ninety-two percent of SES officials come from within government, he said, and only 8 percent change agencies once they reach SES rank.

In phone calls to SES officials at the Bureau of Land Management on Thursday, according to an individual briefed on the matter, BLM acting director Mike Nedd informed them that Zinke liked the idea of moving officials between agencies.

Clement was informed that he would go to the Office of Natural Resources Revenue, which collects royalty payments, according to two individuals familiar with the move, while Fish and Wildlife’s chief of law enforcement, Bill Woody, is slated for the BLM.

The notices were issued by Interior Associate Deputy Secretary James Cason, who also served in Interior under President George W. Bush.

Stier said it would be “appropriate” if Interior officials want to “reallocate the resources of the department against their priorities,” but they are prohibited from targeting employees because of their beliefs or the work they carried out under President Barack Obama.

“It’s one thing to say we’re trying to do different things,” he said “It’s another thing to say they’re going after people for their political views or the policies of the prior administration.”

But one conservative activist said Zinke has done the right thing by putting leaders in place who can carry out President Trump’s agenda at an agency with senior officials “really important to the operations of the place.”

“I think it’s reasonable,” said Chris Edwards, director of tax policy studies at the libertarian Cato Institute. “We all know that government employees can resist action and hope they’re going to wait out the Trump administration. If part of the reason people in, say, ranching states vote for Republicans to get a softer touch [from the government], why wouldn’t the administration put in people who will have a softer touch?”

SEA President Bill Valdez said in an email that “based on the limited information we have right now,” it appears the changes at Interior are “being executed according to applicable law and regulation.”

“SEA will monitor this situation to ensure that these personnel decisions are indeed being lawfully executed and are being made in the best interests of the government and taxpayers,” Valdez wrote.

According to the association’s handbook, the 120-day moratorium on moving senior career staffers “promotes a ‘get acquainted’ opportunity and prevents the reassignment of a career senior executive at the beginning of each new administration, without adequate knowledge of the abilities of the employee involved.”

A reassignment requires a 15-day notice, while a relocation requires a 60-day notice; individuals can move earlier if they waive the right to these time restrictions. SES personnel can appeal their reassignments to the Office of Special Counsel if they think they have been singled out unfairly.

Senior career officials are also being moved at other agencies, in part because of reorganization efforts. At the Energy Department, for example, the Office of International Climate and Technology is being eliminated.

David Sandalow, who served as acting undersecretary of energy under Obama and oversaw the international climate office as the Energy Department’s assistant secretary for policy and international affairs, said in an email that career officials are being unfairly penalized under the new administration.

“Civil servants deserve our thanks, not the disrespect they’re being shown by the Trump administration,” said Sandalow, now the inaugural fellow at Columbia University’s Center on Global Energy Policy. “At Interior, they protect national treasures. At the Energy Department, they invest in innovative technologies. The White House should be supporting their work, not trying to ‘deconstruct the administrative state.’ ”